Achieving Risk and Cost Reductions in CO₂ Geosequestration through 4D Characterisation of Host Formations

Project Summary

The fluid flux is high because the swept volume is low and any changes to the permeability in this region can have significant economic impact in terms of well utilisation efficiency and compression costs. In the far field regions, away from the well, the affected reservoir is much bigger and changes to permeability, through blocking or enhancement, have relatively low impact, though they can still affect the direction of CO₂ plumes over longer time scales.

This project supports Australian CO₂ geosequestration field demonstration and commercial projects by:

• geochemical reaction investigations of the CO₂-H₂O-rock system of target host formations, identifying changes to mineralogy, porosity and permeability, with leading-edge tools and methodology;
• measurement of the anisotropic mechanical properties and permeability of samples, investigating dynamic changes as a result of geochemical reactions; and
• advancing the development of physicochemical and numerical models, to replicate the lab findings of fluid and mass transport, for application at different spatial and time scales.

The experimental and kinetic geochemical modelling studies indicate that the injection of CO₂ into water-bearing reservoirs will reduce the formation water pH and cause dissolution of some minerals. Regarding pore-scale modelling that seeks to track more closely the actual physical transport through the porous media, the in-house extended LBM (XLBM) modelling provides a useful tool for understanding the fluid flow and local changes to the flow architecture at the mesoscale including the porosity change with calcite dissolution and feedback impacts on fluid flow. This, in turn, implies that small components within the samples, be these pore throats or fine particles, may be what is most affected by the applied stress prior to any geochemical reactions taking place.

Key conclusions are:

• Mineral dissolution far outweighs precipitation in the immediate wellbore area. This is usually not taken into account but is commercially important as it influences the decisions about the number and size of the injection wells.
• Near wellbore modelling, even using very conservative simplifying assumptions, shows substantial improvement in injectivity. More comprehensive dynamic modelling will push these predicted results to even bigger (more realistic) increases.
• This is shown to have significant (beneficial) design and commercial consequences.